1. Field of the Invention
The present invention relates to a seal structure between a rotatable member and a stationary member.
2. Description of Related Art
Usually, a mechanical seal is used as a seal between a rotatable member and a stationary member. The mechanical seal structure is selected from various types of seals taking into consideration conditions of use, for example, pressure, temperature, rotational speed, and whether a small amount of leakage is permitted or not, etc.
In the case where the seal is disposed at a slidably contacted portion and is exposed to a relatively high temperature above 200.degree. C. and a relatively low pressure, an O-ring is not usually used. This is because an O-ring is used only as a seal between stationary members or as a seal between a reciprocally movable member and a stationary member, because a high pressure is needed for a portion of the O-ring to be deformed and to enter a clearance between two members, and because a metallic O-ring, which is usually used at high temperatures above about 200.degree. C., has a poor sealing characteristic as compared with a rubber O-ring.
However, because the mechanical seals are designed so as to endure high pressure, high temperature and high rotational speed conditions, they are usually complicated in structure and high in cost.